Process for the preparation of MFI-type zeolitic catalysts

ABSTRACT

The present invention relates to a process for the preparation of zeolitic catalysts of the MFI type in spheroidal form. 
     The process consists in emulsifying and consolidating in paraffinic hydrocarbons, in the presence of a non-ionic surface-active agent or a suitable combination of a non-ionic surface-active agent and a cationic surface-active agent, a dispersion of particles of zeolitic material of the MFI type in a silica sol.

The present invention relates to a process for the preparation ofcatalysts based on MFI-type zeolite in spheroidal form.

More specifically, the present invention relates to a process for thepreparation of catalysts based on MFI-type zeolite active inrearrangement reactions of oximes to amides and suitable for use in gasphase in fluid bed and moving bed reactors.

The invention also relates to the catalysts obtained by means of theabove processes and to the processes in which they are used.

MFI-type zeolites, in particular those with a high silica/alumina ratio(U.S. Pat. No. 4,359,421) and, more generally, those with a low contentof trivalent hetero-elements (patent EP 242,960), are known inliterature as basic materials for the preparation of catalysts which canbe used in numerous reactions and in particular in rearrangementreactions of oximes to amides; among these, particular importance isgiven to reactions carried out in gaseous phase. For example, patent EP234,088 describes a method for the preparation of ε-caprolactamconsisting in putting cyclohexanone-oxime, in the gaseous state, incontact with crystalline alumino-silicates having well-definedphysico-chemical characteristics and preformed in the form of granules(24÷48 mesh).

These materials, however, consisting of the active phase only, havelimited possibilities of being used in industrial reactors; if, in fact,fluid bed or moving bed reactors are to be used for the catalyticprocess, the catalysts should preferably have the form of microspheres,with an average diameter of 30÷100 μm and characterized by a highresistance to interparticle attrition and attrition against the walls ofthe reactors; if, on the other hand, fixed bed reactors are used, thecatalysts should have the typical forms for this technology (spheres,tablets, etc.), with dimensions in the order of several millimeters andcharacterized by a good loading resistance.

The cohesion between the individual particles of the micro-crystallinezeolitic material is generally poor, and consequently the resistance toattrition and loading is usually obtained by combining the zeoliticmaterial with compounds of an inorganic nature (ligands) in the formingphase.

Catalysts based on zeolites, suitable for use in fluid bed or moving bedreactors and with the specific characteristics mentioned above, arewidely described in the known art and are mainly used in catalyticcracking processes (FCC, Fluid Catalytic Cracking catalysts).

In the forming of the above catalysts, normally effected with the knownspray-drying technique, when microspheres with a diameter <100 μm arerequired, silicas and aluminum oxides in the colloidal state orsilico-aluminates are used to give the microspheres a higher resistanceto attrition. The use of these ligands in spherulization processes ofzeolitic materials of the MFI type can however, in some applications,jeopardize their catalytic performances, as these ligands are notentirely inactive in the above reactions.

It is known, for example, that in the catalytic rearrangement reactionof oximes to amides, the presence of ligands significantly jeopardizesthe selectivity of the zeolitic catalyst and the deterioration of thecatalytic performances caused by the formation of organic pitches[Catalysis Letters 17 (1993), 139-140; Catalysis Today 38 (1997),249-253].

To overcome this problem, patent EP 576,295 suggests, for example, thatthe zeolitic material in spherical form be preformed by means ofspray-drying without any addition of ligands and that the microspheresbe subjected, in a subsequent process phase, to thermal treatment inwater to increase their hardness.

In a more recent patent (EP 1,002,577), on the other hand, the use ofsilica ligands is suggested, which, when synthesized by the acidhydrolysis of silicon alkoxides, are practically inert in rearrangementreactions of oximes to amides. With these ligands and by means of aforming process via emulsion, catalysts are obtained in the form ofmicrospheres characterized by a content of silica ligand, expressed asSiO₂, equal to or higher than 30% by weight and by a resistance toattrition suitable for carrying out the rearrangement reaction in fluidbed or moving bed reactors.

Although the silica ligand is practically inert, the high percentage ofSiO₂ in these catalysts tends however to jeopardize the catalyticperformances of the active phase. Furthermore, the forming processdescribed proves to be complex, costly and difficult to develop on atechnologically significant scale.

In the area of forming methods via emulsion, a process has now beenfound which allows catalysts to be obtained in the form of microspheresbased on zeolitic compounds of the MFI type, characterized by a contentof silica ligand (expressed as SiO₂) ranging from 15 to 20% by weight,considerably lower than that of the known compositions of the state ofthe art (≧30% SiO₂).

With respect to these, the reduced concentration of the silica ligandcreates an improvement in the catalytic performances of the materials,increasing their selectivity in the rearrangement reactions of oximes toamides up to values close to the characteristic values of the zeoliticactive phase not formed in spherules; this occurs without jeopardizingthe resistance of the microspheres to attrition which, expressedaccording to the Davison Attrition Index (D.I.) method [“Advances inFluid Catalytic Cracking” Catalytica, Mountain View, Calif., Part 1,1987, page 355], is maintained at the levels (D.I.≦6) normally requiredfor carrying out reactions in gas phase in fluid bed or moving bedreactors.

Another advantage, associated with the low concentration of the silicaligand in the catalytic composition, relating to the productive capacity[Kg*(m³ h)⁻¹] of the catalyst which, expressed as quantity (Kg) of oximeconverted per hour (h) and per volume unit (m³) of catalyst (orcatalytic bed) is increased by at least 10% with respect to that of theknown compositions in the state of the art (EP 1,002,577).

The process of the invention also has the advantage of being lesscomplex, of having a higher productivity and of using a hydrocarbon, asorganic medium, which, in addition to being more economic than thehigher alcohols previously used, can be easily recovered from thereaction mixture.

At the end of the reaction, in fact, a solid phase (corresponding to thecatalyst produced), an aqueous liquid phase (corresponding to whatremains of the aqueous solvent of the hybrid sol) and an organic liquidphase (corresponding to the hydrocarbon used for the emulsion), arepresent in the preparation reactor of the catalyst. The phases tend tostratify naturally in the reactor and can be easily separated; thehydrocarbon can therefore be used again without any purification.

Viceversa, the organic medium (decanol) adopted with the methoddescribed in EP 1,002,577, formed a mixture with the organic base ofwhich the starting mixture (cyclohexylamine and ethanol) consisted, thusrequiring prior purification for re-use.

The process, object of the invention, consists in emulsifying andconsolidating (gelatinizing), in an organic medium and in the presenceof a suitable combination of surface-active agents, a dispersion ofparticles of the zeolitic material in a silica sol having a suitablycontrolled pH.

In particular, the forming process of the catalyst via emulsion/gelationcomprises the following steps:

-   a) preparation of a silica sol by the hydrolysis of silicon    alkoxides in an aqueous medium and under acid conditions;-   b) mixing of the silica sol with an aqueous dispersion of MFI-type    zeolite particles;-   c) basification of the hybrid sol (b) up to values not higher than    pH 6.0;-   d) emulsification/gelation of the hybrid sol in paraffinic,    cycloparaffinic or aromatic hydrocarbons, in the presence of a    non-ionic surface-active agent or a suitable combination of a    non-ionic and a cationic surface-active agent.

Whereas passages a) and b) of the process relating to the preparation ofthe hybrid sol do not differ from what is known in the state of the art(for example patent EP 1,002,577), passages c) and d) represent theinnovative aspect of the process, object of the invention, as they aredeterminant in minimizing the quantity of silica ligand in the catalyticcomposition, without comprising its morphological-granulometriccharacteristics and resistance to attrition.

In particular, in the process, object of the invention, theconsolidation (gelation) of the micro-drops of hybrid sol (b) emulsifiedin the organic medium, is controlled by the combined action of the pH(step c) and of the cationic surface-active agent: whereas the pH of thehybrid sol regulates its gelation kinetics, the presence of the cationicsurface-active agent in the emulsifying medium allows the sol-geltransition to be controlled, preventing, in this phase of the process,the production of strong interparticle aggregation phenomena withnegative effects on the morphology of the materials.

It is known that in processes via emulsion/gelation of silica sol inparaffinic hydrocarbons, it is necessary to operate in the presence ofemulsifying agents (surface-active agents) of the non-ionic typecharacterized by HLB (Hydrophile-Lipophile-Balance) values of less than9, among which sorbitan monooleate (HLB 4.3) is one of the most wellknown in the state of the art (Nat. Academy Press, “Using Oil SpillDispersants on the Sea” Chap. 2—Chemistry and Physics of Dispersants andDispersed Oil pages 28-80 (1989)).

In the process, object of the invention, the use of surface-activeagents with these physico-chemical characteristics may not be sufficientto control the morphology of the materials; this is due toflocculation/aggregation phenomena which arise during the consolidationof the micro-drops of hybrid sol dispersed in the emulsifying medium. Inthese cases, this drawback can be overcome by using, in a combinationwith the non-ionic emulsifying agent, a cationic surface-active agent(quaternary ammonium salt) of the type [N R₁ R₂ R₃ R₄]⁺ X⁻ wherein X isCl, Br and R₁ R₂ R₃ R₄ are C_(n)H_(2n+1) alkyl groups, the same ordifferent, with 1≦n≦18.

The use of hexadecyltrimethylammonium bromide (or cetyltrimethylammoniumbromide; R₁, R₂, R₃═CH₃; R₄═C₁₆H₃₃; X═Br) combined with the non-ionicsurface-active agent sorbitan monooleate (Span 80, trade-name)characterized by HLB=4.3, has proved to be particularly suitable for thepurpose.

By means of this morphological control method, it has been possible tospherulize catalytic compositions based on MFI-type zeolites containingthe silica ligand in a quantity ranging from 15 to 20% by weight(expressed as SiO₂) at the same time maintaining a resistance toattrition equivalent to or higher than that which can be obtained withother known techniques in the state of the art, in the presence of amuch higher quantity of ligand, for example higher than 30% by weight.In particular, these catalytic compositions consist of microspheres withan average diameter varying from 30 to 200 μm and characterized by aresistance to attrition, expressed as D.I. (Davison Index)<6.0. Thesecharacteristics are extremely suitable for rearrangement reactions ofoximes to amides in gas phase in fluid bed or moving bed reactors.

The process is based on the use of a hybrid sol (particles of MFI-typezeolite dispersed in a silica sol) prepared with the technique known inthe state of the art, as described for example in patent EP 1,002,577.

In the preparation of silica oligomers (silica sol, step a) siliconalkoxides, such as tetra-ethylorthosilicate (TEOS), are used as silicaprecursors. The hydrolysis of these compounds in an aqueous mediumcatalyzed by acids, together with the effect of the hydrolysisconditions on the physico-chemical characteristics of silica oligomersare widely described in the state of the art [C. J. Brinker, G. W.Sherer “Sol-Gel Science. The Physic and Chemistry of sol-gelprocessing”, Academic Press Inc., 1990].

Silica oligomers suitable for the purposes of the invention arepreferably obtained by the hydrolysis of TEOS in an aqueous medium andin the presence of mineral acids, such as, for example, HCl and HNO₃,the molar ratio H₂O/TEOS being regulated to between 10 and 25 and the pHbetween 1.5 and 3.0. The hydrolysis reaction is carried out maintainingthe reagents (TEOS and acid aqueous solution) under mechanical stirringfor times normally varying from 1 to 3 hours at temperatures usuallyranging from 20 to 40° C. The concentration of alcohol in the finalreaction mixture (in particular ethanol deriving from the hydrolysis ofTEOS) can be suitably adjusted in a subsequent operation.

The solution of silica oligomers, for example, can be dealcoholated andconcentrated by distillation at reduced pressure and at temperatureslower than 30° C.

Zeolitic compounds of the MFI type which can be used for the purposes ofthe present invention can be selected from Silicalite-1 or zeolitescontaining aluminum or other trivalent or tetravalent hetero-atoms, suchas, for example, those of Group III (B, Ga, In) or Ti.

In particular, zeolitic compounds of the MFI type suitable for therearrangement reaction of oximes to amides can be selected fromSilicalite-1 or zeolites with a low content of aluminum (molar ratioSi/Al>1000) or of other hetero-atoms (molar ratio Si/hetero-atom>1000).As described in the state of the art, these materials are obtained byhydrothermal synthesis from a mixture of reagents comprising a highpurity silica precursor (for example TEOS), water, alcohols, organicamines or cations of tetraalkyl-ammonium (R_(n)N⁺) as crystallizationcontrol (templating agents) of the zeolitic material.

The reaction product, consisting of individual micro-crystallineparticles, having dimensions normally lower than 1 μm, is generallyseparated from the mother liquor by centrifugation, repeatedly washedwith water to remove the excess templating agent and finally dried andcalcined. Alternatively, the reaction product can be spray-dried.

In the preparation process of the catalysts, object of the presentinvention, the zeolitic intermediate centrifuged and optionally washedwith water, is advantageously used.

In the process according to the invention, the zeolitic material isdispersed in an aqueous medium, using mechanical dispersing agents oralso with ultrasonic devices, the dispersion conditions being controlledso that the dimensions of the materials reach values close to those ofthe individual particles (normally lower than 1 μ). In the process,object of the invention, the zeolitic intermediate centrifuged andoptionally washed with water, in the form of thickened product, isadvantageously and preferably used. The control of the dispersion degreeof the zeolitic material in the aqueous medium is particularly importantif dried zeolitic intermediates and, above all, zeolitic materialssubjected to thermal treatment at a temperature ≧500° C., are used inthe process.

Under the preferred conditions in which the centrifuged and optionallywashed zeolitic intermediate is used, the pH of the resulting aqueoussolution is normally alkaline due to the incomplete removal of thetemplating agent. To avoid the appearance of undesired polymerization orgelation phenomena of the acid silica oligomers in the subsequent mixingoperation, the above dispersions are acidified to pH values lower thanor equal to 5.0.

The acidification can be effected with solutions of mineral or organicacids and, under the preferred conditions, with the type of acid used inthe preparation of the silica ligand, such as HCl and HNO₃. The quantityof acid is preferably controlled so that the pH of the resultingligand/zeolite mixture (hybrid sol, step b) is lower than 4.0, morepreferably ranging from 2.0 to 3.0.

With respect to the composition of the above mixture, the weight ratiobetween the zeolitic compound of the MFI type and the silica ligand(both expressed as SiO₂) can be extended to values of 5.5 inclusive,thus obtaining catalytic compositions in which the minimum content ofsilica ligand is about 15% by weight; in the preferred compositions, thecontent of silica ligand ranges from about 20% by weight to about 15% byweight.

The concentration of MFI-type zeolite in the aqueous solution of thesilica ligand normally ranges from 15 to 25% by weight.

The hybrid sol deriving from step b) is subsequently (step c)) basifiedto a definite pH value.

The objective of this operation is to control the consolidation(gelation) rate of the micro-drops dispersed in the organic emulsifyingmedium. In order to obtain materials with suitablemorphological-granulometric characteristics, the pH of the hybrid sol israised up to a value not higher than 6.0 and, preferably, within a rangeof values between 5.2 and 5.8. Operating under the preferred pHconditions, the gelation time normally ranges from 15 to 60 minutes.

The basification of the hybrid sol is usually carried out at roomtemperature by the addition of an aqueous inorganic or organic basesolution, preferably a solution of ammonium hydroxide, for example 1 M.

The emulsification/gelation operation of the hybrid sol (step d)) iseffected in paraffinic or aromatic hydrocarbons in the presence of apair of non-ionic and cationic surface-active agents.

Among the paraffinic hydrocarbons having general formula C_(n)H_(2n+2),compounds with values of n varying from 6 to 16, are generally used,such as, for example, n-hexane, n-decane, n-hexadecane or their isomersor mixtures of more easily available and economic hydrocarbons (forexample ligroins with boiling point of 60÷100, Kerosenes), orcycloparaffinic compounds (for example, cyclohexane). Among aromatichydrocarbons, which are less preferred than paraffinic hydrocarbons,toluene and xylenes, for example, can be used.

Surface-active agents with HLB (Hydrophile-Lipophile-Balance) valueslower than 9 are normally used as emulsifying agents of the non-ionictype; sorbitan mono-esters with an HLB varying from 4 to 7 arepreferably used, in particular sorbitan monooleate (trade-name Span 80,HLB 4.3).

Quaternary ammonium salts of the type [N R₁ R₂ R₃ R₄]⁺ X⁻ wherein X═Cl,Br and R₁ R₂ R₃ R₄═C_(n)H_(2n+1) alkyl groups, the same or differentwith 1≦n≦18, are used as cationic surface-active agents.

Hexadecyltrimethylammonium bromide (or cetyltrimethylammonium bromide;R₁ R₂ R₃ ═CH₃; R₄═C₁₆H₃₃, X═Br) combined with the non-ionicsurface-active agent sorbitan monooleate, is particularly suitable forthe purpose. The concentration of the latter in the organic emulsifyingmedium normally ranges from 5 g/l to 15 g/l, whereas the concentrationof cetyltrimethylammonium bromide (CTMABr) is usually ≧0.3 g/l and isregulated so that the weight ratio Span 80/CTMABr ranges from 10 to 40,preferably from 15 to 25.

In the emulsification operation in the presence of the above pair ofsurface-active agents, the volumetric ratio between the continuous phase(hydrocarbon) and the dispersed phase (hybrid sol) is normally ≧2.5 and,preferably, ranging from 3.0 to 5.0.

The emulsification/gelation temperature of the hybrid sol, generallyranging from 20 to 25° C., can vary within a wide range of values inrelation to the chemical nature of the emulsifying medium. For example,in decane, the operation can be carried out at a temperature rangingfrom 15 to 50° C.; to avoid the consolidation (or gelation) of thehybrid sol occurring too rapidly (at a T of ˜50° C.) or too slowly (at aT of ˜15° C.) under these temperature limit conditions, suitablecorrections must be made to the pH of the hybrid sol, so that thegelation time is ≧15 minutes or less than an hour. As is known in thestate of the art, the control of the dimensions of the microspheres, forexample from 30 to 200 μm, can be effected by acting on the rotationrate of the stirrer of the emulsification reactor and/or on theviscosity of the emulsifying medium.

After gelation of the hybrid sol and in order to complete itsconsolidation, the dispersion of the microspheres in the emulsifyingmedium is maintained under stirring for at least 0.5 hours and generallyfor times ≦3 hours. The separation of the material is then effected,following the operations and procedures-known in the state of the art.For example, after filtration, the catalyst is washed with organicsolvent (for example with alcohols, such as ethanol, propanol andisopropanol, or ketones, such as acetone), subsequently dried (forexample, at room temperature or at T≦110° C.) and finally calcined in anoxidizing atmosphere (air) at temperatures higher than 450° C., normallywithin the temperature range typical of zeolitic materials (500÷550°C.), with a heating rate normally in the order of 50° C./h and for timesin the order of 1÷10 hours, preferably for 4÷8 hours.

The materials prepared with the above procedure consist of microsphereswhose dimensions can vary from 30 to 200 μm in relation to theemulsification conditions of the ligand/zeolite mixture. Thesematerials, as a result of their morphological-granulometric andphysico-chemical characteristics specified above, can be convenientlyused in processes for the preparation in gas phase of amides by means ofthe catalytic rearrangement of oximes.

Among amides which, as is known, form an important group ofintermediates, ε-caprolactam is of particular importance, especially forthe preparation of polyamide resins and synthetic fibres.

In particular, the catalysts, object of the invention, can beadvantageously used in the rearrangement reaction of cyclohexanone-oximeto ε-caprolactam with a process in gas phase, consisting in bringingcyclohexanone-oxime vapours in contact with the catalyst.

Following the technique known in the state of the art (EP 1,002,577),this reaction, for example, can be carried out at a pressure rangingfrom 0.05 to 10 bars and at a temperature ranging from 250 to 500° C.,preferably from 300 to 450° C.

More specifically, the cyclohexanone-oxime is fed to a reactorcontaining the catalyst, in vapour phase and in the presence of one ormore solvents and, optionally, also an uncondensable gas.

Under the preferred conditions, the cyclohexanone-oxime is dissolved ina mixture of solvents, subsequently described, at a concentrationranging from 5 to 25% by weight and preferably from 6 to 15%; thesolution thus obtained is then vaporized and fed to the reactor.

Preferred solvents are of the R₁—O—R₂ type wherein R₁ is a C₁-C₄ alkylchain and R₂ can be a hydrogen atom or an alkyl chain containing anumber of carbon atoms lower than or equal to R₁.

Alcohols with a C₁-C₂ alkyl chain are particularly preferred. Thesesolvents can be used alone or mixed with each other, or combined with anaromatic hydrocarbon such as benzene or toluene.

The feeding rate of the cyclohexanone-oxime is controlled so that theWHSV (Weight Hourly Space Velocity) value, expressed as kg ofcyclohexanone-oxime/(kg of catalyst*h), ranges from 0.1 to 50 h⁻¹,preferably from 0.5 to 20 h⁻¹.

In said reaction, the catalysts, object of the invention andcharacterized by a high content in active phase (≧80%), have highercatalytic performances than those of the materials (max. 70% of activephase) known in the state of the art and synthesized with silica ligandsof the same physico-chemical nature (EP 1,002,577). In particular, oncarrying out the reaction under identical WHSV conditions (referring tothe weight of active component in the catalyst), the composition richerin active phase positively influences the selectivity of the reaction toε-caprolactam.

Some illustrative and non-limiting examples are provided hereunder for abetter understanding of the present invention and for its embodiment.

EXAMPLE 1 Preparation of Silicalite-1

The preparation is described of Silicalite-1, active phase of thecatalyst.

632 g of an aqueous solution at 20% of Tetra-propylammonium hydroxide(TPAOH) are charged into a 3 litre Pyrex reactor, flushed with nitrogen.555 g of Tetra-ethylorthosilicate (TEOS) are added dropwise, over aperiod of about 5 hours, under stirring and flushing with nitrogen. Thefollowing day, the solution is closed in a 5 litre autoclave inside aTeflon container. Three washings are effected with nitrogen at about 10atm. The hydrothermal synthesis is then carried out at 140° C. for 24hours with stirring at 80 revs/minute.

The solid dried with a spray-dryer is separated from part of thesuspension obtained. The suspension, coming from the synthesis,containing the zeolite, is fed to the spray-dryer at a rate of 1.5litres/hour, and an inlet temperature of 230° C.

The solid recovered is kept dry, without undergoing further treatment.

Another aliquot of suspension is centrifuged, separating the solidproduct, which is washed with distilled water until the washing waterreaches pH≈7. The product obtained is kept humid and is spherulized asdescribed in the following examples.

Part of the centrifuged solid is dried at 120° C., calcined at 550° C.for 4 h and subsequently sieved at a size of 42÷80 mesh for thecatalytic activity test (Example 6).

The X-ray diffraction of the calcined product identifies the product asMFI zeolite.

Chemical analysis carried out by means of ICP-AS shows low contents ofNa, K, Al, Fe (<30 ppm).

Morphological analysis of the material, carried out by means of ASAP2000 (nitrogen absorption isotherm at 77K), gives the following result:A.S.E.=55.1 m²/g, micropore volume=0.183 cm³/g, mesopore volume=0.264cm³/g.

The bulk density of the catalyst sieved at a size of 42÷80 mesh, is 0.63g/cm³.

The catalysts thus prepared must be subjected to a forming process toacquire the necessary characteristics (spherical shape, mechanicalresistance) for use in fluid bed or moving bed reactors.

EXAMPLE 2 Preparation of the Hybrid Sol of Silicalite-1 and Silica Sol

The preparation is described of a hybrid sol of Silicalite-1 and Silicasol, an intermediate for the preparation of composite materialcontaining 80% by weight of Silicalite-1.

A. Preparation of the silica ligand (silica sol).

213 g of TEOS (Aldrich; titer 98%), 285 g of demineralized water and 3.0g of HCl 1N are charged into a 1000 cm³ cylindrical reactor equippedwith a mechanical stirrer, thermometer and external cooling bath. Thereagents are kept under stirring at a temperature of 25÷30° C. for thetime necessary for obtaining a limpid solution (about 35 minutes); thestirring is then continued for a further 120 minutes. The acid silicasol thus obtained (pH=2.5; titer SiO₂=11.97%) is preserved in arefrigerator at 5° C. until the moment of use.

B. Preparation of the hybrid sol. The intermediate product (titer ofSilicalite-1=75.6%), centrifuged and washed, as described in Example 1,is used as Silicalite precursor. 19.9 g of the precursor (equal to 15.04g of Silicalite-1) are dispersed for 120 minutes in 50 cm³ ofdemineralized water by means of a Teflon anchor magnetic stirrer and,subsequently, for a further 15 minutes with an ultrasonic probe(Sonifier, Cell Disruptor B15; Branson).

The aqueous suspension of Silicalite-1 is acidified from pH≈10.5 topH=2.5 with a solution of HCl 1N and then mixed with 31.2 g of thesilica sol A) for about 3 minutes by means of a magnetic stirrer.

C. Basification of the hybrid sol. The pH of the hybrid sol prepared inB) is subsequently brought to a value of 5.7 by the dripping of a 1Msolution of NH₄OH in ˜2÷3 minutes; a small aliquot (3÷4 cm³) of thehybrid sol is conserved in a test-tube to measure the gelation time.

EXAMPLE 3 Preparation of a Microspheroidal Catalyst Consisting ofSilicalite-1 and Silica

The preparation is described of a Silicalite-1/Silica composite materialcontaining 80% by weight of Silicalite-1, using the hybrid sol ofExample 2.

D1. Emulsification/gelation. The hybrid sol (˜100 cm³) is transferred toa cylindrical reactor (internal diameter 100 mm, volume 1000 cm³)previously charged, at a temperature of 23° C., with 400 cm³ of asolution of 10 g/l of sorbitan monooleate (Span 80; Fluka) and 1 g/l ofhexadecyltrimethylammonium bromide (Aldrich) in n-decane (Fluka, titer98%); the mechanical stirrer with 6 radial blades is then activated,regulating its velocity at 500 revs per minute. After ˜20 minutes, thehybrid sol consolidates; the stirring is continued for a further 60minutes, regulating the velocity at 350 revs per minute, and the solidis then left to deposit, for about 60 minutes. The thickened product isfiltered and washed with acetone; after drying at room temperature, thematerial is calcined in an oxidizing atmosphere (air) at 550° C. for 4hours with a heating rate of 50° C./h.

The composite material thus obtained contains 80% by weight ofSilicalite-1.

The median diameter (D50) of the microspheres, measured with a CoulterLS130 apparatus, is equal to 100 μm.

The resistance to attrition of the catalyst of Example 3 was verifiedaccording to the Davison Attrition Index (D.I.) method [“Advances inFluid Catalytic Cracking” Catalytica, Mountain View, Calif., Part 1,1987, page 355] and proved to be in line with the values of a freshcatalyst according to the specification of use in a FCC reactor(D.I.<6).

EXAMPLE 4 Preparation of a Microspheroidal Catalyst Consisting ofSilicalite-1 and Silica

The preparation is described of a Silicalite-1/Silica composite materialcontaining 80% by weight of Silicalite-1, as an alternative to thatdescribed in Example 3, using the hybrid sol of Example 2.

D2. Emulsification/gelation. The same procedure is adopted as in Example3, varying the quantities of sorbitan monooleate, equal to 10 g/l, andhexadecyltrimethylammonium equal to 0.75 g/l in the solution ofn-decane.

The composite material thus obtained contains 80% by weight ofSilicalite-1.

The median diameter (D50) of the microspheres is equal to 90 μm.

The resistance to attrition of the catalyst of Example 4 was verifiedand proved to be D.I.<6.

EXAMPLE 5 Preparation of a Microspheroidal Catalyst Consisting ofSilicalite-1 and Silica

The preparation is described of a Silicalite-1/Silica composite materialcontaining 80% by weight of Silicalite-1, as an alternative to thosedescribed in Examples 3 and 4, using the hybrid sol of Example 2.

D3. Emulsification/gelation. The same procedure is adopted as in Example3, with a different hydrocarbon solution. In this case 400 g of n-hexaneare used (Fluka, titer 98%) containing 8.5 g/l of sorbitan monooleate.

The composite material thus obtained contains 80% by weight ofSilicalite-1.

The resistance to attrition of the catalyst of Example 5 was verifiedand proved to be D.I.<6.

EXAMPLE 6 Catalytic Activity Tests of Silicalite-1, Active Phase of theCatalyst

The operating procedure is described for the catalytic activity testwith Silicalite-1, active phase of the catalyst.

The catalyst described in Example 1 (sieved at a size of 42÷80 mesh) wastested in a fixed bed tubular reactor having a length equal to 200 mmand a diameter of 11.5 mm. A thermocouple sheath having ø_(ext.)=4 mmwas positioned inside the reactor. 0.5 grams of catalyst diluted withquartz up to a volume of 2 cm³ are charged into the reactor andpositioned in the central part of the reactor between two layers ofquartz.

The cyclohexanone-oxime (CEOX) is fed in solution with toluene, methanoland water. The CEOX solution is preheated before being charged into thereactor and vaporized and mixed with nitrogen directly in the reactorbefore coming into contact with the catalyst.

Before carrying out the test, the catalyst is heated to the reactiontemperature in a stream of nitrogen and dried. It is then treated withthe mixture of solvents alone before being used in the reaction. Thetest begins by sending the CEOX solution onto the catalyst.

The mixture of effluent vapours from the reactor is condensed andsamples are collected for evaluating the catalytic performances. Thesamples are analyzed by gaschromatography and the catalytic performancesare evaluated by calculating the conversion of CEOX and selectivity toε-caprolactam (CPL).

Table 1 indicates the operating conditions and catalytic performances atthe 1^(st) and 20^(th) hour of the test in the rearrangement reaction ofCEOX to CPL.

EXAMPLES 7-8-9 Catalytic Activity Tests of Microspheroidal CatalystsConsisting of Silicalite-1 and Silica

The catalytic activity tests are described, with Silicalite-1 and silicacomposite materials.

The catalysts described in Examples 3-4-5 were tested as described inExample 6. In order to respect the same WHSV, the different tests wereeffecting by varying the catalyst charge and then the contact time.

Tables 2-3-4 indicate the catalytic performances at the 1^(st) and20^(th) hour of the test.

COMPARATIVE EXAMPLE 1 Preparation of a Microspheroidal CatalystConsisting of Silicalite-1 and Silica According to the ProcedureDescribed in Patent EP 1,002,577)

The preparation is described of a Silicalite-1/Silica composite materialcontaining 70% by weight of Silicalite-1.

A. Preparation of the Silica Ligand (Silica Sol).

213 g of TEOS (Aldrich; titer 98%), 285 g of demineralized water and 3.0g of HCl 1N are charged into a 1000 cm³ cylindrical reactor equippedwith a mechanical stirrer, thermometer and external cooling bath. Thereagents are kept under stirring at a temperature of 25÷30° C. for thetime necessary for obtaining a limpid solution (about 35 minutes); thestirring is then continued for a further 60 minutes. The acid silica solthus obtained (pH=2.5; titer SiO₂=11.98%) is preserved in a refrigeratorat 5° C. until the moment of use.

B. Preparation of the hybrid sol. The product, washed and thickened, asdescribed in Example 1 (titer of Silicalite-1=75.6%), is used asSilicalite-1 precursor. 15.9 g of the precursor (equal to 12.0 g ofSilicalite-1) are dispersed for 60 minutes in 60 cm³ of demineralizedwater by means of a Teflon anchor magnetic stirrer and, subsequently,for a further 15 minutes with an ultrasonic probe (Sonifier, CellDisruptor B15; Branson); after dilution with 60 cm³ of ethanol, theultrasonic treatment is continued for a further 10 minutes.C. Basification of the hybrid sol. The hydro-alcohol suspension ofSilicalite-1, consisting of particles with an average diameter of 0.22μm (Coulter analyzer, Model N4, 5D), is subsequently acidified frompH≈10.5 to pH=2.5 with a solution of HCl 1N and is then mixed with 43 gof the silica sol A) for about 3 minutes by means of a magnetic stirrer.D. Emulsification/gelation. The mixture thus obtained (about 185 cm³) istransferred to a cylindrical reactor (internal diameter 100 mm, volume1000 cm³) previously charged with 500 cm³ of 1-decanol (Fluka, titer98%); the mechanical stirrer with 6 radial blades is then activated,regulating its velocity at 800 revs per minute. After 10 minutes, theemulsion is rapidly discharged from the bottom of the reactor into anunderlying container containing 300 cm³ of a solution at 10% (v/v) ofcyclohexylamine (Aldrich, titer 99%) in 1-decanol, the stirring beingmaintained at room temperature. The stirring is continued for a further60 minutes; the solid is then left to deposit, for about 60 minutes, andis subsequently filtered and repeatedly washed with ethanol. Afterdrying at room temperature, the composite material is calcined in anoxidizing atmosphere (air) at 550° C. for 4 hours with a heating rate of50° C./h.

The composite material thus obtained contains 70% by weight ofSilicalite-1.

The median diameter (D50) of the microspheres, measured with a CoulterLS130 apparatus, is equal to 50 μm.

The resistance to attrition of the catalyst of Comparative Example 1 wasverified according to the Davison Attrition Index (D.I.) method andproved to be in line with the values of a fresh catalyst according tothe specification of use in a FCC reactor (D.I.<6).

COMPARATIVE EXAMPLE 2 Catalytic Activity Tests of the MicrospheroidalCatalyst consisting of Silicalite-1 and Silica, containing 70% by Weightof Silicalite-1

The catalyst described in Comparative Example 1 was tested as in Example6. In order to respect the same WHSV, the test was effected varying thecatalyst charge and, then, the contact time.

Table 5 indicates the catalytic performances at the 1^(st) and 20^(th)hour of the test.

TABLE 1 OPERATING CONDITIONS Temperature (° C.) 350 WHSV (h⁻¹) (*) 4.5Contact time (s) (#) 0.11 CEOX partial pressure (bar) 0.034 MeOH/CEOX(molar ratio) 10 Toluene/CEOX (molar ratio) 10 N₂/CEOX (molar ratio) 8H₂O/CEOX (molar ratio) 0.15 Catalyst charge (g) 0.5 CATALYTICPERFORMANCES Catalyst of Example 1 Time (h) 1 20 CEOX conversion (%)99.8 75.3 Selectivity to CPL (%) 93.6 95.4 Rearrangement reactorproductivity 2.8 (kg CEOX fed/(h * litre catalyst) (*) WHSV refers forthe feeding to CEOX alone and for the catalyst to the active phasealone. (#) The contact time refers to the whole feeding mixture and tothe composite catalyst.

TABLE 2 CATALYTIC PERFORMANCES ($) Catalyst of Example 3 Time (h) 1 20CEOX conversion (%) 99.4 76.8 Selectivity to CPL (%) 93.0 94.1Rearrangement reactor productivity 2.3 (kg CEOX fed/(h * litre catalyst)($) The operating conditions used are the same as those indicated inTable 1

TABLE 3 CATALYTIC PERFORMANCES ($) Catalyst of Example 4 Time (h) 1 20CEOX conversion (%) 99.2 77.0 Selectivity to CPL (%) 93.2 94.4Rearrangement reactor productivity 2.3 (kg CEOX fed/(h * litre catalyst)($) The operating conditions used are the same as those indicated inTable 1

TABLE 4 CATALYTIC PERFORMANCES ($) Catalyst of Example 5 Time (h) 1 20CEOX conversion (%) 99.9 88.6 Selectivity to CPL (%) 92.9 94.8Rearrangement reactor productivity 2.3 (kg CEOX fed/(h * litre catalyst)($) The operating conditions used are the same as those indicated inTable 1

TABLE 5 CATALYTIC PERFORMANCES ($) Catalyst of Comparative Example 1Time (h) 1 20 CEOX conversion (%) 99.7 84.7 Selectivity to CPL (%) 91.593.2 Rearrangement reactor productivity 2.0 (kg CEOX fed/(h * litrecatalyst) ($) The operating conditions used are the same as thoseindicated in Table 1

1. A method for the preparation in gas phase of an amide, comprisingcatalytic arrangement of an oxime in the presence of a catalyticcomposition, wherein the catalytic composition is based on an MFI-typezeolite in the form of microspheres with an average diameter rangingfrom 30 to 200 μm, containing a quantity of silica ligand ranging from15 to 20% by weight, having a resistance to attrition, expressed asDavison Index<6.0, and wherein the catalytic composition is obtained bya process comprising: a) hydrolyzing silicon alkoxides in an aqueousmedium and under acid conditions, thereby forming a silica sol; b)mixing the silica sol with an aqueous dispersion of MFI-type zeoliteparticles; c) adjusting the pH of the hybrid silica sol obtained in step(b) to a pH value not higher than 6.0; and d) emulsifying/gelating thehybrid sol in paraffinic, cycloparaffinic or aromatic hydrocarbons, inthe presence of a non-ionic surface-active agent or a suitablecombination of a non-ionic and cationic surface-active agent, whereinthe amide is ε-caprolactam and the oxime is cyclohexanone-oxime.
 2. Themethod according to claim 1, wherein the zeolitic compounds of the MFItype are selected from Silicalite-1 or zeolites containing aluminum orother trivalent or tetravalent hetero-atoms.
 3. The method according toclaim 2, wherein the zeolitic compounds of the MFI type are selectedfrom Silicalite-1 or zeolites wherein the molar ratio Si/Al orSi/trivalent or tetravalent hetero-atoms is >1000.
 4. The methodaccording to claim 1, wherein the average particle diameter of themicrospheres ranges from 90 to 100 μm.
 5. The method according to claim2, wherein the zeolitic compounds contain trivalent or tetravalenthetero-atoms selected from Group III and Ti.
 6. The method according toclaim 1, wherein the non-ionic surface-active agent comprises anon-ionic surface-active agent having an HLB of lower than
 9. 7. Themethod according to claim 6, wherein the non-ionic surface-active agentcomprises a sorbitan monoester having an HLB of from 4 to
 7. 8. Themethod according to claim 7, wherein the sorbitan monoester is sorbitanmonoleate.
 9. The method according to claim 1, wherein the cationicsurface-active agent comprises a quatemary ammonium salt.
 10. The methodaccording to claim 9, wherein the quaternary ammonium salt compriseshexadecyltrimethylammonium bromide.
 11. The method according to claim 1,wherein step (d) is carried out in the presence of a mixture of (1)sorbitan monoleate and (2) hexadecyltrimethylammonium bromide.
 12. Themethod according to claim 11, wherein (1) and (2) are present in aweight ratio of from 10 to
 40. 13. The method according to claim 12,wherein the weight ratio is from 15 to
 25. 14. The method according toclaim 13, wherein the hydrocarbon is a continuous phase and the hybridsol is the dispersed phase, and the volumetric ratio between thecontinuous phase and the dispersed phase is ≧2.5.
 15. The methodaccording to claim 14, wherein the volumetric ratio is from 3.0 to 5.0.16. The method according to claim 1, wherein the pH is adjusted in step(c) to a value from 5.2 to 5.8.
 17. The method according to claim 1,wherein the hybrid silica sol obtained in step (b) has a pH lower than4.0.
 18. The method according to claim 17, wherein the pH ranges from2.0 to 3.0.